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South America Weather Forecast: Gastrointestinal Disease Likely

Climate scientists predict that climate change will lead to increased variability in precipitation over much of South America. Research by Carlton et al (2013) on residents of northwestern rural Ecuador who rely on streams and rivers for their drinking water shows how those changes might impact water quality and associated rates of diarrhea, a water-related disease which leads to approximately 1 million deaths of young children worldwide each year. The study further highlighted curious dynamics involving precipitation and water-borne disease.

While previous research in the region (Levy, 2009) found that drinking water quality was generally worse in the rainy season, it varied more on a daily or even hourly basis than between seasons. To further investigate the connections between water and health, the same researchers investigated the relationships between diarrhea incidence and rainfall over the prior 8 weeks, the propensity of communities to treat their drinking water before consumption as well as their water and sanitation conditions.

The researchers found that heavy rainfall events (a 24-hour rainfall total that exceeded the 90th percentile value) were associated with an increased risk of diarrheal disease (incidence rate ratio = 1.39, 95% confidence interval: 1.03, 1.87), but only after a dry period. After wet periods, the risk of diarrhea actually decreased with such heavy rainfall events (incidence rate ratio = 0.74, 95% confidence interval: 0.59, 0.92). They found that the presence of improved sanitation and hygiene infrastructure did not have a significant effect on these rates, but that the prevalence of water treatment in a community did seem to help.

Based on their 2009 and 2013 studies, researchers concluded that pathogens can become concentrated during dry periods and can be washed into waterways by heavy rainfall events. Following wet periods, however, heavy rainfall can dilute these same waterways thereby decreasing the opportunities for transmission.

Based on these results, it is clear that weather can have a significant yet complex effect on water quality and diarrheal disease for resourced-limited communities, not just in rural South America for all of the estimated 1.1 billion people around the world who depend on unimproved drinking water sources. With the predicted increase of precipitation variability (Marengo, 2009), it is likely that diarrhea rates will increase in this region although future research will be needed to quantify this relationship.